Field Day is a great time to demonstrate the
amazing capabilities of high-altitude balloon payloads. Each year I try
to fly something different that we can show to the public at the
Huntsville Amateur Radio Clubís Field Day site. The site is uniquely
positioned in a field next to Space Camp, which always attracts quite a
number of curious Space Campers and their families. Iíve found that
balloon flights into near space definitely get their attention.

Since Field Dayís main goal (in addition to
the goal of eating tons of great food!) is to demonstrate emergency
communications, this year I flew a 2-meter FM simplex voice repeater.
From its vantage point over 100,000 feet above the Earth, this repeater
would cover a great majority of the Southeast and Midwest. What better
way to demonstrate wide-area emergency communications using low-power
ground stations?

Simplex Repeater

A simplex repeater is a fairly easy thing to
put together, consisting of just two things: a handheld radio and a
voice record/playback unit. A few years ago, RadioShack sold a great
module that made this a plug-n-play solution. Sadly, it discontinued the
unit, so Iíve been relying on the increasingly rare eBay find for these.
Fortunately, Scott Miller, N1VG, of Argent Data Systems (http://www.argentdata.com/catalog/)
stepped in to fill the gap and introduced the ADS-SR1 simplex repeater
module at the Dayton Hamventionģ this year (see photo 1). Scott added
quite a few bells and whistles to his version. Through touch-tone
commands, you can set up voice and CW ID announcements, voice-mailboxes,
and a host of other features, including up to 218 seconds of record
time. However, due to the amount of traffic expected through the
repeater, I chose to limit the record and playback time to 24-second
intervals. Just hook up the interconnect cable from the ADS-SR1 to your
handheld radio (I recommend using Evereadyģ lithium AA batteries),
adjust the audio levels for best audio quality, stuff it all into a
StyrofoamTM box with lots of duct tape, and youíre ready to fly.

Although you can use the simplex repeater
module with any HT (Argent makes a variety of interface cables for
various HT models), Iíve had great results with several of the Alinco
family. The dual-band Alinco DJ-C7T is very easy to interface and is
very lightweight and rugged. Since it has an SMA connector, I find that
the Comet SMA-24 whip antenna works well with it. However, I do
recommend powering the DJ-C7T from an external 6-volt lithium battery
pack for maximum operating time and to also increase the output power to
500 mW. Another Alinco radio Iíve had great success with for balloon
flights is the very inexpensive and lightweight DJ-S11T. You wonít need
an external battery pack for this radio, since itís already designed to
use internal AA batteries. I once lost a payload carrying two of these
radios. Seven months after my flight, a hunter found it lying in a mud
puddle covered in fire ants. I powered up the radios and they worked
just fine after months of abuse.

However, I do have one recommended
modification if you plan to use a DJ-S11T. The tiny whip antenna that
comes permanently installed in the radio is terribly inefficient. I
usually remove it and just solder two 19-inch wires to the antenna pads
inside the radio and then tape the wires to a small wood or carbon-fiber
dowel rod taped to the side of the radio to create a half-wave vertical
dipole. You could also just install an SMA connector instead to use an
antenna of your choice. In either case, youíll be amazed at the
difference. Photo 2 shows the DJ-S11T with the vertical dipole
modification.